Pacotes recebidos não atingem a cadeia INPUT do iptables

Question

Estou executando um cliente VPN em um contêiner docker. Estou tentando conectar-me do host a um servidor da Web em execução no contêiner do Docker pela porta 8080. Quando tento conectar-me, vejo meu pacote de entrada na porta 8080 via tcpdump, mas o servidor da Web nunca o vê. Eu adicionei as regras do iptables '-j LOG' para todas as possíveis transições de estado do pacote para tentar rastreá-lo. Eu vejo o pacote em:

• tabela 'raw', cadeia PREROUTING
• tabela 'mangle', cadeia PREROUTING
• table'nat ', cadeia PREROUTING

e depois ... nada. Após um pequeno atraso, o pacote é reenviado e vejo o novo pacote passar por PREROUTING. Nada aparece nas cadeias mangle INPUT ou mangle FORWARD - que, até onde eu sei, é impossível - tem que acertar uma delas. Existe alguma maneira de um pacote passar por PREROUTING, mas não acertar INPUT ou FORWARD? Meus iptables estão abaixo:

root@87ff7ad8e4f9:/# iptables -t raw -L 
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             tcp spt:http-alt nflog-prefix  "raw pre-route Src incoming packet"
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "raw pre-route Dest incoming packet"

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "Dest outgoing packet"
NFLOG      tcp  --  anywhere             anywhere             tcp spt:http-alt nflog-prefix  "Src outgoing packet"
root@87ff7ad8e4f9:/# iptables -t mangle -L 
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "mangle PREROUTING Dest incoming packet"

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
NFLOG      all  --  anywhere             anywhere             nflog-prefix  "mangle INPUT Dest incoming packet any2"

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
NFLOG      all  --  anywhere             anywhere             nflog-prefix  "mangle FORWARD Dest incoming packet any"

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
MARK       tcp  --  anywhere             anywhere             tcp spt:http-alt MARK set 0x1
MARK       tcp  --  anywhere             anywhere             tcp dpt:http-alt MARK set 0x1
NFLOG      tcp  --  anywhere             anywhere             tcp spt:http-alt nflog-prefix  "MARK set 0x1"
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "Dest MARK set 0x1"

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
root@87ff7ad8e4f9:/# iptables -t nat -L 
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "nat PREROUTING Dest incoming packet"

Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "nat INPUT Dest incoming packet"

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination         
root@87ff7ad8e4f9:/# iptables -t filter -L 
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         
NFLOG      tcp  --  anywhere             anywhere             nflog-prefix  "connection made"
NFLOG      tcp  --  anywhere             anywhere             tcp dpt:http-alt nflog-prefix  "filter INPUT Dest incoming packet"

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             172.17.0.0/16       
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain
ACCEPT     tcp  --  anywhere             anywhere             owner GID match vpn
ACCEPT     udp  --  anywhere             anywhere             owner GID match vpn
DROP       all  --  anywhere             anywhere            

E meu syslog mostra:

Oct  4 07:22:56 87ff7ad8e4f9 raw pre-route Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39119 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 
Oct  4 07:22:56 87ff7ad8e4f9 mangle PREROUTING Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39119 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 
Oct  4 07:22:56 87ff7ad8e4f9 nat PREROUTING Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39119 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 
Oct  4 07:22:57 87ff7ad8e4f9 raw pre-route Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39120 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 
Oct  4 07:22:57 87ff7ad8e4f9 mangle PREROUTING Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39120 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 
Oct  4 07:22:57 87ff7ad8e4f9 nat PREROUTING Dest incoming packet IN=eth0 OUT= MAC=02:42:ac:11:00:02:02:42:2e:2c:fd:2e:08:00 SRC=76.167.254.196 DST=172.17.0.2 LEN=60 TOS=00 PREC=0x00 TTL=63 ID=39120 DF PROTO=TCP SPT=46644 DPT=8080 SEQ=4027056663 ACK=0 WINDOW=29200 SYN URGP=0 MARK=0 

    

Answer 1

Eu não entendo completamente o porquê, mas o filtro Reverse Path foi a causa dos pacotes descartados. Desligá-lo através do seguinte comando resolveu o meu problema: sysctl -w net.ipv4.conf.eth0.rp_filter = 0

    

Answer 2

Eu acho que entendi. O que há entre PREROUTING e INPUT / FORWARD? Veja o mapa : a decisão de roteamento.

De seus registros: SRC=76.167.254.196 DST=172.17.0.2 . Você não pode rotear o endereço IP público para privado sem o DNAT. Tente adicionar isso:

iptables -t nat -A PREROUTING -i eth0 -p tcp --dport 8080 -j DNAT --to-destination 172.17.0.2

Ou você pode configurar sua VPN para ter um IP privado.